package com.qh.xx.circle;

/**
 * @description:
 * @author: zqh
 * @date: 2021/11/5 12:45
 **/
public class CircleQueue<E> {
    private int front;
    private int size;
    private E[] elements;
    private static final int DEFAULT_CAPACITY = 10;

    public CircleQueue() {
        elements = (E[]) new Object[DEFAULT_CAPACITY];
    }

    public int size(){
        return size;
    }

    public boolean isEmpty(){
        return size == 0;
    }

    public void enQueue(E element){
        ensureCapacity(size + 1);
       elements[(front + size) % elements.length] = element;
       size++;
    }

    public E deQueue(){
        E frontElement = elements[front];
        elements[front] = null;
        front = (front + 1) % elements.length;
        size--;
        return frontElement;
    }

    public E front(){
        return elements[front];
    }

    @Override
    public String toString() {
        StringBuilder string = new StringBuilder();
        string.append("capcacity=").append(elements.length)
                .append(" size=").append(size)
                .append(" front=").append(front)
                .append(", [");
        for (int i = 0; i < elements.length; i++) {
            if (i != 0) {
                string.append(", ");
            }

            string.append(elements[i]);
        }
        string.append("]");
        return string.toString();
    }

    /**
     * 索引封装
     * @param index
     * @return
     */
    private int index(int index) {
        index += front;
        return index - (index >= elements.length ? elements.length : 0);
    }

    /**
     * 保证要有capacity的容量
     * @param capacity
     */
    private void ensureCapacity(int capacity) {
        int oldCapacity = elements.length;
        if (oldCapacity >= capacity) {
            return;
        }

        // 新容量为旧容量的1.5倍
        int newCapacity = oldCapacity + (oldCapacity >> 1);
        E[] newElements = (E[]) new Object[newCapacity];
        for (int i = 0; i < size; i++) {
            newElements[i] = elements[index(i)];
        }
        elements = newElements;

        // 重置front
        front = 0;
    }
}
